1. Field of the Invention
This invention relates to an optical disk player wherein an optical disk on which information signals, such as audio and/or video signals, are recorded is irradiated with a laser beam for reading out and reproducing the information signals.
2. Description of the Prior Art
Optical disk players are becoming more and more popular, partly due to their superior reproduction capacities and partly due to their reduced size as compared to players for other types of disks.
An optical disk player generally has a disk table driven by a spindle motor. An optical disk is inserted into the disk player and affixed to this disk table for rotation therewith. An optical pick-up including a semi-conductor laser is adapted to travel in a direction across a series of substantially circular concentric tracks recorded on the disk. The laser beam emitted from the semiconductor laser is directed onto a surface of the optical disk at right angles thereto so as to scan the tracks for reading out and reproducing the information signals recorded in the tracks.
In an optical disk player of the above type, the information signals, such as audio signals, in the form of a number of pulse coded bit strings, are recorded with high density on the optical disk used as the signal recording medium. A standard disk size having a diameter of 12 cm. has been adopted as the "compact disk" for prerecorded musical or audio signals. Since this "compact" optical disk has such a small size and is used as the standard recording medium for the optical disk players designed for playback of prerecorded musical or audio signals, an effort has been made to similarly reduce and standardize the size of the optical disk player itself. For example, in order to minimize the height or thickness of the optical disk player, the optical pick-up may be arranged so that the laser beam is emitted from the laser in a direction parallel with the surface of the optical disk affixed to the disk table and at right angles with the optical axis of an object lens by which the laser beam is eventually focused at the surface of the optical disk. Some of the optical components, such as lenses, 1/4 wave plates etc., may be arranged along this direction parallel with the disk surface so that the required thickness or height of the optical disk player is reduced. The laser beam is then reflected 90.degree. by a mirror and transmitted towards the object lens which converges the laser beam and directs it vertically towards the surface of the optical disk. The object lens also receives the laser beam reflected back from the disk surface. Such optical pick-up in which the laser beam is emitted from the semi-conductor laser in a direction normal to the optical axis of the object lens has a lesser thickness than one in which for example, the laser beam is emitted from the laser in a direction aligned with the optical axis of the object lens.
As mentioned above, it is desirable to reduce the size of the base and/or outer casing of optical disk players and the arrangement of the optical pick-up may be conducive to reducing the thickness or height of the overall device. Conventional optical disk players are usually provided with a rectangular casing and the optical pick-up is mounted for movement in a direction normal to a side of the rectangular casing along a radius of the optical disk on the disk table so that the record tracks on the disk are scanned by the laser beam for reproducing the information signals recorded in the tracks.
In this type of conventional disk player, the optical pick-up is provided with a biaxial driving device for the object lens for effecting servo control of the object lens along two mutually perpendicular or orthogonally related axes, that is, in the directions for focusing the laser beam at the plane of the tracks on the optical disk, and for accurately positioning the laser beam in the tracking or radial direction. This biaxial driving device and the mounting for the object lens tend to be bulky. Therefore, when the optical pick-up is transferred to a position for scanning the outermost track on the optical disk, the optical pick-up projects substantially beyond the outer periphery of the optical disk. Thus, the side of the outer casing normal to the direction of travel of the optical pick-up must be spaced substantially outward from the perimeter of the optical disk and it has not been possible to reduce the outer casing to the size of a rectangle inscribed by the circular perimeter of the optical disk, that is, to reduce the optical disk player to the smallest size possible.